737 Engine Stabilization for Takeoff

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Boeing has issued a reminder to operators in a Fleet Team Digest (737NG-FTD-02-18001) to pass on to their crews about the correct procedure for setting takeoff thrust. It follows 8 confirmed aborted takeoff events in 2017 resulting from advancing the throttles before engines were allowed to stabilize at 40% N1.

Boeing say that following a review of the flight data by CFM or Boeing, the root cause for these events was the engines not being stabilized at 40 percent N1, prior to advancing the thrust levers to takeoff thrust (autothrottle TO/GA).
The recommended procedure for setting takeoff thrust begins by manually positioning thrust levers to approximately 40% N1, which allows the engines to accelerate and stabilize at an intermediate thrust setting. This minimizes asymmetrical thrust when TO/GA is selected. If the intermediate thrust setting overshoots 40% N1 speed, it is not necessary to reduce N1 down to 40%. TO/GA can be selected after the engines stabilize at 40% N1.

“Allowing the engines to stabilize provides uniform engine acceleration to takeoff thrust and minimizes directional control problems. This is particularly important if crosswinds exist or the runway surface is slippery. The exact initial setting is not as important as setting symmetrical thrust. If thrust is to be set manually, smoothly advance thrust levers toward takeoff thrust.

Note: Allowing the engines to stabilize for more than approximately 2 seconds before advancing thrust levers to takeoff thrust may adversely affect takeoff distance.”

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